Method for operating a floor cleaning machine

ABSTRACT

A method for operating a floor cleaning machine on a floor surface. The floor cleaning machine includes a cleaning-liquid container, a dirty-liquid container, a chassis for moving the floor cleaning machine over the floor surface, a cleaning means and a dirty-liquid take-up means. The method includes: sensing an amount of cleaning liquid supplied from the cleaning-liquid tank to the cleaning means within a first time interval while moving the floor cleaning machine; sensing an amount of dirty liquid being removed from the dirty-liquid take-up means to the dirty-liquid container within a second time interval while moving the floor cleaning machine; comparing the sensed amount of cleaning liquid against a first threshold value; comparing the sensed amount of dirty liquid against a second threshold value; outputting a first fault signal if the sensed amount of cleaning liquid is greater than the first threshold value and the sensed amount of dirty liquid is less than the second threshold value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit and priority of German Patent Application No. 10 2022 111 605.0, filed May 10, 2022, the disclosure of which is incorporated by reference as if fully set forth in detail herein.

FIELD

The present disclosure relates to a method for operating a floor cleaning machine.

BACKGROUND

Such floor cleaning machines are known from the prior art. In the operation of such machines, cleaning liquid such as, for example, fresh water from the cleaning-liquid container is applied to the floor surface to be cleaned by the cleaning means, the cleaning elements engaging with the floor surface in order to release dirt from it by acting in combination with the cleaning liquid. The previously applied cleaning liquid, loaded with dirt following the engagement of the cleaning elements with the floor surface, so that it is dirty liquid, is taken back up by the dirty-liquid take-up means, which may be designed, for example, as a suction foot, and transferred into the dirty-liquid container.

Such so-called scrubber-drier machines may be embodied as manually operated or ride-on machines. In addition, it is possible for such machines to be embodied as autonomous so-called cleaning robots, such that no operator directly supervises the operation.

However, the following problems can occur in the operation of such machines.

If cleaning liquid is applied to the floor surface to be cleaned but the dirty-liquid take-up means is not working reliably, cleaning liquid loaded with dirt, i.e., dirty liquid, remains on the floor surface to be cleaned. On the one hand, this represents a safety risk, as there is then an increased danger of slipping on the floor surface. On the other hand, the desired cleaning result is not achieved.

Furthermore, such floor cleaning machines often have a suction-extraction means such as a suction turbine, which is driven by an electric motor. This generates an air flow from the dirty-liquid take-up means, which may then be designed as a suction foot, for example, to the dirty-liquid container, with dirty liquid being entrained in the take-up means by this air flow and conveyed into the dirty-liquid container. If the motor current of the electric motor drops while the voltage remains constant, this can usually have two causes. Firstly, it is possible that the connection between the dirty-liquid take-up means and the dirty-liquid container is blocked, such that there is no longer any air flow from the dirty-liquid take-up means into the dirty-liquid container, and as a result the suction-extraction means has to convey less air, such that the motor current is reduced. There is therefore a fault present.

Alternatively, however, there may be so much liquid in the dirty-liquid take-up means that ambient air is prevented from entering the take-up means, which likewise prevents air flow from occurring. This is not a fault condition, however; this state ceases when the liquid present in the take-up means has been drawn off into the dirty-liquid container due to the negative pressure. However, the two cases described above cannot be differentiated on the basis of the measurement of the motor current alone. In particular, it is not possible to determine on this basis whether or not there is a fault.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

Proceeding from the prior art, the object of the present disclosure is therefore to provide a method for operating a floor cleaning machine, and to provide such a machine, by which method and machine faults can be reliably detected during operation.

According to a first aspect of the present disclosure, this object is achieved by a method for operating a floor cleaning machine, the floor cleaning machine comprising a cleaning-liquid container, a dirty-liquid container and a chassis for moving the floor cleaning machine over a floor surface to be cleaned, the floor cleaning machine comprising a cleaning means having cleaning elements designed to engage with the floor surface to be cleaned, the cleaning means being connected to the cleaning-liquid container for the purpose of supplying cleaning liquid to the cleaning means and being designed to apply cleaning liquid to the floor surface to be cleaned, the floor cleaning machine having a dirty-liquid take-up means that, for the purpose of removing dirty liquid from the dirty-liquid take-up means to the dirty-liquid container, is connected to the latter and designed to take up dirty liquid from the floor surface to be cleaned, the method comprising the following steps: moving the floor cleaning machine over a floor surface to be cleaned; sensing, as it moves, the amount of cleaning liquid being supplied from the cleaning-liquid tank to the cleaning means within a first time interval; sensing, as it moves, the amount of dirty liquid being removed from the dirty-liquid take-up means to the dirty-liquid tank within a second time interval; comparing the sensed amount of cleaning liquid against a first threshold value; comparing the sensed amount of dirty liquid against a second threshold value; outputting a first fault signal if the sensed amount of cleaning liquid is greater than the first threshold value and the sensed amount of dirty liquid is less than the second threshold value.

In the case of the method of the present disclosure, it is on the one hand sensed during operation, i.e., while the machine is moving over a floor surface to be cleaned, whether cleaning liquid is being applied by the cleaning means to the floor surface to be cleaned. This is effected in that the amount of cleaning liquid applied is sensed in a first time interval by a suitably designed means, and compared against a threshold value. The threshold value may be selected to be very low or even zero. However, comparison against a non-zero threshold value ensures that low measurement values of the means do not automatically lead to the result that cleaning liquid is actually being supplied to the floor surface via the cleaning means.

Furthermore, a further means is used to sense the amount of dirty liquid that is being removed from the dirty-liquid take-up means and transferred into the dirty-liquid container during a second time interval.

The first and second time intervals in this case may coincide, i.e. the sensing may be effected simultaneously, or the second time interval lags behind the first time interval in order to take account of the fact that the cleaning liquid applied to the floor surface to be cleaned can only be taken back up by the dirty-liquid take-up means after a time delay.

The sensed amount of dirty liquid taken up is compared against a second threshold value, which may likewise be selected to be very low or even zero. But here, too, the threshold value comparison ensures that the factors already described do not occur.

Finally, in the case of the method of the present disclosure, a fault signal is output if, on the one hand, the amount of dispensed cleaning liquid sensed during the first time interval is above the threshold value, and the amount of removed dirty liquid sensed during the second time interval is below the threshold value. It is thus sensed that the dirty-liquid take-up means is not operating reliably.

This is either indicated to a user on the basis of the fault signal, or the fault signal is used to switch off a drive, possibly present, of the floor cleaning machine via which the chassis is driven and the floor cleaning machine is moved over the floor surface to be cleaned.

The method of the present disclosure is advantageous in particular when used together with an autonomous floor cleaning machine, since there a user cannot immediately detect that there is dirty liquid remaining on the floor surface to be cleaned, and the user can then actively stop the cleaning travel. In contrast to the prior art, a malfunction of the dirty-liquid take-up means is reliably detected automatically during operation.

In one embodiment, the floor cleaning machine comprises a suction-extraction means that applies negative pressure to the dirty-liquid tank and comprises an electric drive motor that, in operation, is supplied with a voltage of a predefined magnitude, such that a supply current flows through the drive motor, the intensity of the supply current being sensed in a third time interval, the sensed intensity of the supply current being compared against a third threshold value, the sensed amount of dirty liquid being compared against a fourth threshold value, and a second fault signal being output if the sensed intensity of the supply current is less than the third threshold value and the sensed amount of dirty liquid is less than the fourth threshold value.

In the case of this embodiment of the method according to the invention, in addition to the motor current of the suction-extraction means, it is also sensed whether dirty liquid is being transferred into the dirty-liquid container. It is only if the latter is not the case that the second fault signal is output. This is because, in this case, there is obviously a malfunction that is due to a blockage in the cable between the dirty-liquid take-up means and the dirty-liquid container.

However, if dirty liquid is still being conveyed into the dirty-liquid container when the motor current is too low, the condition for the second fault signal is not fulfilled, since there is obviously no malfunction, but rather the dirty liquid itself is causing only a small air flow, or even no air flow, to be conveyed by the suction-extraction means, which also results in a reduction in the motor current.

In the case of this embodiment, therefore, not only is the motor current of the suction-extraction means alone used to detect a malfunction, but this is effected in combination with sensing of the amount of dirty liquid conveyed into the dirty-liquid container.

It is to be noted at this point that it is an independently inventive concept to sense both the motor current of the suction-extraction means and the amount of dirty liquid transferred into the dirty-liquid container in a time interval and then to output a fault signal if both the amount of dirty liquid conveyed and the motor current are below a predefined threshold value.

In particular, the floor cleaning machine may comprise a means designed to sense the amount of cleaning liquid supplied from the cleaning-liquid tank to the cleaning means within a first time interval, and a means designed to sense the amount of dirty liquid removed from the dirty-liquid take-up means to the dirty-liquid tank within a second time interval. In addition, there may also be provided a means designed to sense the intensity of the supply current in a third time interval.

In another embodiment, the cleaning-liquid container and the cleaning means are connected by a cleaning-liquid pipe for the purpose of supplying cleaning liquid, a flow sensor being provided, in the cleaning-liquid pipe, as a means for sensing the amount of cleaning liquid supplied in the first time interval. The use of a flow sensor in the pipe is a reliable way of sensing the amount of cleaning liquid in question.

As an alternative to the flow sensor or in addition to it, it is likewise possible for a cleaning-liquid pump to be provided, in the cleaning-liquid pipe, that is designed to sense the amount of cleaning liquid supplied to the cleaning means in the first time interval, such that the pump acts as a means for sensing the amount of cleaning liquid supplied from the cleaning-liquid tank to the cleaning means within a first time interval. In this case, there is no need to provide yet another sensor in addition to the pump. If yet another sensor is provided, a redundant system is provided that remains functional even if one of the two means for sensing the flow rate fails.

In another embodiment, a first means is provided for the purpose of sensing the level in the cleaning-liquid container, the amount of cleaning liquid supplied in the first time interval being sensed, by the first means, by sensing of a change in the level in the cleaning-liquid container in the first time interval. In this case, the amount of cleaning liquid supplied to the cleaning means is determined by a change in the level in the cleaning-liquid container. This can be easily realized technically in terms of equipment. In particular, this may be realized in that, the first means, for the purpose of sensing the level in the cleaning-liquid container, comprises a float, the change in the position of the latter in the first time interval being sensed in order thereby to sense the amount of cleaning liquid supplied in the first time interval.

If a second means is provided, for the purpose of sensing the level in the dirty-liquid container, the amount of cleaning liquid supplied in the first time interval being sensed, by the second means, by sensing of a change in the level in the dirty-liquid container in the second time interval. Thus, in the case of this embodiment, the amount of dirty liquid removed into the dirty-liquid container is likewise determined from a change in the level therein. In this case, the second means, for the purpose of sensing the level in the dirty-liquid container, can be designed as a pressure sensor.

Finally, in a further aspect of the present disclosure, the above object is achieved by a floor cleaning machine designed to execute the method according to the disclosure as described above.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 shows a schematic sectional representation of an exemplary embodiment of a floor cleaning machine according to the disclosure.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary embodiment of a floor cleaning machine 1 according to the disclosure, which is designed to execute an embodiment of a method according to the disclosure for operating such a machine.

As can be seen from FIG. 1 , the floor cleaning machine 1 has a chassis 5, comprising a plurality of wheels 3, by which the floor cleaning machine 1 can be moved over a floor surface 7 to be cleaned. In this case, in the exemplary embodiment shown here, the floor cleaning machine 1 has a drive 8, not represented in more detail, by which the rear wheels 3 of the chassis 5 are driven, such that the floor cleaning machine 1 can move automatically over the floor surface 7 to be cleaned. In addition, the floor cleaning machine 1 represented here is realized as a so-called robot, i.e., it can move autonomously over the floor surface 7 to be cleaned without being guided by a user, and automatically detects obstacles and determines its course based thereon.

However, the present disclosure is not limited to such robots, but may be applied to any type of floor cleaning machine 1, i.e., also to so-called ride-on machines or machines where the user walks behind the machine.

As is further shown in FIG. 1 , the floor cleaning machine 1 has a cleaning means 9, which comprises a cleaning element 11 realized here as a brush driven in rotation, which in operation engages with the floor surface 7 to be cleaned. The cleaning means 9 is also designed in such a way that the cleaning element 11 can be raised relative to the floor surface 7 to be cleaned, such that the cleaning element 11 then does not engage with the floor surface 7 to be cleaned.

As can also be seen from FIG. 1 , the cleaning means 9 has an outlet 13, which is connected via a cleaning-liquid pipe 15 to a cleaning-liquid container 17 that is accommodated in a housing 19 of the floor cleaning machine 1. Provided in the cleaning-liquid pipe 15 there is flow sensor 21, which constitutes a means by which the amount of cleaning liquid flowing through the cleaning-liquid pipe 15 and supplied to the cleaning means 9 in a time interval can be sensed.

Additionally provided in the cleaning-liquid pipe is a pump 23, which is designed to convey cleaning liquid from the cleaning-liquid container 17 to the outlet 13, and thus to the cleaning means 9. The pump 23 in this case may be designed in such a way that it likewise senses the amount of cleaning liquid conveyed from the cleaning-liquid container 17 to the outlet 13 in a time interval. This may be in addition to the flow sensor 21 or as an alternative to it. If both the pump 23 and the flow sensor 21 can sense the amount conveyed per time interval, a redundant system is achieved.

Furthermore, or in addition to the flow sensor 21 and the pump 23, there may be provided in the cleaning-liquid container 17 a first means that is configured to sense the height of the level 25 of the cleaning liquid in the cleaning-liquid container 17. This means comprises a guide element 27, which extends substantially in a vertical direction in the cleaning-liquid container 17 when the floor cleaning machine 1 is positioned on a horizontal floor surface 7 to be cleaned. A float 29, the position of which can be sensed, is guided on the guide element 27. On the basis of the change in position of the float 29 of this float means 27, 29 within a time interval, the amount of cleaning liquid that has been supplied to the cleaning means 9 during this time interval can then also be determined.

Finally, as an alternative to the flow sensor 21, the pump 23 or the float means 27, 29, or in addition thereto, a first pressure sensor 31 may be provided in the base region of the cleaning-liquid tank 17, the signal of which sensor is a measure of the gravity pressure of the cleaning liquid in the cleaning-liquid container 17. Thus, by means of this first pressure sensor 31, it is then also possible to determine, or sense, the cleaning liquid supplied to the cleaning means 9 in a time interval.

It can also be seen from FIG. 1 that, in the housing 19, the floor cleaning machine 1 also has a dirty-liquid container 33, the upper region of which is connected to the inlet of a suction-extraction means 35 that is driven by an electric motor 37, which can include a so-called suction turbine in which the electric motor 37 drives a fan wheel in rotation. The suction-extraction means is thus designed to apply a negative pressure, relative to the environment of the floor cleaning machine 1, to the dirty-liquid container 33. Finally, the electric motor 37 is designed, or provided with a corresponding means, such that a signal can be generated that is a measure of the current drawn by the electric motor 37. Thus, a signal can be generated that represents the amount of motor current drawn by the electric motor 37 in a time interval.

Furthermore, it can be seen from FIG. 1 that a second and a third pressure sensor 39, 41 are provided in the dirty-liquid container 33. The second pressure sensor 39 is designed to sense the gravity pressure of the dirty liquid in the base region of the dirty-liquid container 33, and to generate a corresponding signal. The third pressure sensor senses the pressure above the level 43 of the dirty liquid in the dirty-liquid container 33, since this pressure is lowered relative to the ambient pressure due to the suction-extraction means 35. The level 43 in the dirty-liquid container 33 can then be determined in a known manner from the signals of the second and the third pressure sensor 39, 41. Furthermore, the change in the level 43, and thus the amount of dirty liquid supplied to the dirty-liquid container 33 in a time interval, can be determined.

It is to be noted at this point that the present disclosure is not limited to the level 43 in the dirty-liquid container 33, and thus the amount of dirty liquid supplied in a time interval, being determined by means of pressure sensors. Alternative solutions are also conceivable here, such as, for example, the use of a float.

As can be also seen from FIG. 1 , the upper region of the dirty-liquid container 33 is connected via a dirty-liquid pipe 45 to a dirty-liquid take-up means 47, which in the exemplary embodiment represented here is realized as a so-called suction foot. The suction foot has a front sealing lip 49, which has slots extending away from the region in which it rests against the floor surface 7 to be cleaned, and a rear sealing lip 51, which is not slotted. The sealing lips 49, 51 and the suction foot extend substantially across the width of the floor cleaning machine 1, and the region between the sealing lips 49, 51 is connected to the dirty-liquid container 33 via the dirty-liquid pipe 45, and is thus subjected to a negative pressure when the suction-extraction means 35 is in operation. As a result of this negative pressure, dirty liquid on the floor surface 7 to be cleaned is sucked into the dirty-liquid container 33.

If the dirty-liquid pipe 45 is blocked or if the space between the sealing lips 49, 51 of the dirty-liquid suction means 47 is completely filled with dirty liquid, such that no ambient air can enter this space, the suction-extraction means 35 only has to convey a small amount of air to maintain the negative pressure in the dirty-liquid container 33. This means that, in these situations, the motor current of the electric motor 37 that drives the suction-extraction means 35 is reduced compared to normal operation.

Finally, it can be seen that the floor cleaning machine 1 has a controller 53 that is connected via lines to the electric motor 37, the float means 27, 29, the pump 23, the flow sensor 21, the drive 7 and the pressure sensors 31, 39, 41, such that the aforementioned components can transmit their signals to the controller 53.

This signal connection allows the flow sensor 21, the pump 23, the float means 27, 29 and the first pressure sensor 31 each to transmit to the controller 53 a signal that is a measure of the amount of cleaning liquid supplied in a first time interval from the cleaning-liquid container 17 to the outlet 13, and thus to the cleaning means 9. Similarly, the second pressure sensor 39 and the third pressure sensor 41 may likewise transmit to the controller 53 a signal that is a measure of the amount of dirty-liquid taken up by the dirty-liquid take-up means 47 and removed into the dirty-liquid container 33 in a second time interval.

The exemplary embodiment of a floor cleaning machine 1 described above may be operated in the manner described below.

The floor cleaning machine 1 is moved, by means of the chassis 5 and the drive 8, over the floor surface 7 to be cleaned, this being effected automatically in the present case, and the controller 53 also determining by means of sensors, not represented, a route along which the floor cleaning machine 1 cleans the floor surface 7 to be cleaned. During this process, cleaning liquid is supplied continuously by means of the pump 23 from the cleaning-liquid container 17, through the cleaning-liquid pipe 15, into the region of the cleaning means 9. By means of the driven cleaning element 11, dirt is then released from the floor surface to be cleaned while the floor cleaning machine 1, as viewed in FIG. 1 , moves further to the right, such that the cleaning liquid loaded with dirt, and thus the dirty liquid, then passes into the region of the dirt take-up means 47. At the same time as the cleaning liquid is being supplied, the suction-extraction means 35 with the electric motor 37 connected to it is also in operation, such that a negative pressure is generated in the dirty-liquid container 33. Due to this negative pressure, dirty liquid that passes into the region of the dirty-liquid take-up means 47, and thus between the sealing lips 49, 51, is extracted by suction through the dirty-liquid pipe 45 and removed into the dirty-liquid container 33, provided that the dirty-liquid pipe 45 is not blocked or that there is no other malfunction of the dirty-liquid take-up means 47.

While the floor cleaning machine 1 is moving over the floor surface 7 and while cleaning liquid is being applied and dirty liquid is being removed, the following steps are always carried out repeatedly.

During a first time interval, the amount of cleaning liquid applied to the floor surface 7 to be cleaned is sensed by means of the flow sensor 21. As an alternative to the flow sensor 21, this may also be effected by means of the pump 23, by the float means 27, 29 or the first pressure sensor 31, in the manner already described. The sensing of this amount during the first time interval is effected on the basis of the signal respectively transmitted to the controller 53. In this case, the signal from the flow sensor 21, the pump 23, the float means 27, 29 and/or the first pressure sensor 31 may be integrated in the controller 53 during the first time interval, such that the integrated signal is then a measure of the cleaning liquid applied to the floor surface 7 to be cleaned during the first time interval.

Similarly, during a second time interval, the amount of dirty liquid removed into the dirty-liquid container 33 during this second time interval is sensed by means the second and third pressure sensors 39, 41 and the signals generated by them. In this case, too, this amount may be determined by integration of the respective signals. In particular in this case, the signal of the third pressure sensor 41 is subtracted from that of the second pressure sensor 39 in order to take into consideration the effect of the negative pressure prevailing above the level 43 in the dirty-liquid container 33.

The first time interval and the second time interval can be offset in time with respect to each other in such a way that the second time interval starts somewhat later than the first time interval. It is also possible, however, for the time intervals to run in parallel. However, if the first alternative is used, this takes into consideration that, due to the movement of the floor cleaning machine 1, there must always be a certain period of time between the application of a certain amount of cleaning liquid and the removing of exactly this amount.

Finally, the signal of the motor current of the electric motor 37 of the suction-extraction means 35 is also sensed during the second time interval, and this likewise may be effected by integration of the current signal in the controller 53.

If the signal representing the amount of cleaning liquid applied is greater than a first threshold value, this indicates that cleaning liquid is actually being applied to the floor surface 7 to be cleaned. Then, if the amount of dirty liquid removed during the second time interval is below a second threshold, a sufficient amount of dirty liquid is not being removed even though cleaning liquid is being applied. Therefore, if the amount of cleaning liquid applied during the first time interval exceeds the first threshold value and during the check the amount of dirty liquid removed during the second time interval is below the second threshold value, this indicates a malfunction, and the controller outputs a first fault signal. Such a malfunction may be caused, for example, by the sealing lips 49, 51 of the dirty-liquid take-up means 47, designed as a suction foot, being in a worn condition, such that there is not sufficient negative pressure being generated in the suction foot, or by the dirty-liquid pipe 45 between the dirty-liquid take-up means 47 and the dirty-liquid container 33 being cracked or leaking. The fault signal may be used, for example, to stop the drive 8, such that the floor cleaning machine 1 stops. This prevents cleaning liquid from being applied to larger regions of the floor surface to be cleaned without the dirty liquid being removed again. In addition, the first fault signal may be used to switch off the pump 23.

It is also checked whether the amount of dirty liquid removed during the second time interval, or the signal generated on the basis of it, is below a third threshold value. If at the same time the motor current of the electric motor 37, or the signal based on it, is also below a fourth threshold value, this indicates that either the dirty-liquid pipe 45 or the dirty-liquid take-up means 47 is blocked, such that no dirty liquid can pass into the dirty-liquid container 33. This is likewise a malfunction, and in this case the controller 53 generates a second fault signal, which in turn can be used to stop the drive 8 and/or the pump 23.

If, however, the motor current signal is below the fourth threshold value, but at the same time the signal for the amount of dirty liquid removed during the second time interval is above the third threshold value during the second time interval, this indicates that the dirty-liquid take-up means 47 is completely filled with dirty-liquid, such that there can be no air flow through the dirty-liquid pipe 45. In this case, therefore, the low motor current is not associated with a malfunction, and also no fault signal is generated by the controller 53.

The exemplary embodiment of the operating method according to the present disclosure for the floor cleaning machine 1 thus allows reliable sensing of malfunctions in which dirty liquid would remain on the floor surface 7 to be cleaned. Furthermore, the parallel sensing of the motor current and of the amount of dirty liquid removed also enables the signal of the motor current of the electric motor 37 likewise to be used for fault determination.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

List of Reference Signs 1 floor cleaning machine 3 wheel 5 chassis 7 floor surface to be cleaned 8 drive 9 cleaning means 11 cleaning element 13 outlet 15 cleaning-liquid pipe 17 cleaning-liquid container 19 housing 21 flow sensor 23 pump 25 level of cleaning liquid 27 guide element 29 float 31 first pressure sensor 33 dirty-liquid container 35 suction-extraction means 37 electric motor 39 second pressure sensor 41 third pressure sensor 43 level of dirty liquid 45 dirty-liquid pipe 47 dirty-liquid take-up means 49 front sealing lip 51 rear sealing lip 53 controller 

What is claimed is:
 1. A method for operating a floor cleaning machine (1) on a floor surface (7), the floor cleaning machine (1) comprising a cleaning-liquid container (17), a dirty-liquid container (33), a chassis (5) for moving the floor cleaning machine (1) over the floor surface (7), a cleaning means (9) and a dirty-liquid take-up means (47), the cleaning means (9) having cleaning elements (11) configured to engage with the floor surface (7), the cleaning means (11) being connected to the cleaning-liquid container (17) for the purpose of supplying cleaning liquid to the cleaning means (11) and being configured to apply cleaning liquid to the floor surface (7) to be cleaned, the dirty-liquid take-up means (47) that is connected to the dirty-liquid container (33) and configured to transmit dirty liquid from the floor surface (7) to the dirty-liquid container (33), the method comprising: moving the floor cleaning machine (1) over the floor surface (7), sensing, as it moves, the amount of cleaning liquid being supplied from the cleaning-liquid tank (17) to the cleaning means (11) within a first time interval, sensing, as it moves, the amount of dirty liquid being removed from the dirty-liquid take-up means (47) to the dirty-liquid container (33) within a second time interval, comparing the sensed amount of cleaning liquid against a first threshold value, comparing the sensed amount of dirty liquid against a second threshold value, outputting a first fault signal if the sensed amount of cleaning liquid is greater than the first threshold value and the sensed amount of dirty liquid is less than the second threshold value.
 2. The method according to claim 1, the floor cleaning machine (1) comprising a suction-extraction means (35) that applies negative pressure to the dirty-liquid tank (33) and comprises an electric drive motor (37) that, in operation, is supplied with a voltage of a predefined magnitude, such that a supply current flows through the drive motor (37), the intensity of the supply current being sensed in a third time interval, the sensed intensity of the supply current being compared against a third threshold value, the sensed amount of dirty liquid being compared against a fourth threshold value, and a second fault signal being output if the sensed intensity of the supply current is less than the third threshold value and the sensed amount of dirty liquid is less than the fourth threshold value.
 3. The method according to claim 1, the floor cleaning machine (1) comprising a means designed to sense the amount of cleaning liquid supplied from the cleaning-liquid tank (17) to the cleaning means (11) within a first time interval, and the floor cleaning machine (1) comprising a means designed to sense the amount of dirty liquid removed from the dirty-liquid take-up means (47) to the dirty-liquid container (33) within a second time interval.
 4. The method according to claim 2, the floor cleaning machine (1) comprising a means designed to sense the intensity of the supply current in a third time interval.
 5. The method according to claim 1, wherein the chassis (5) of the floor cleaning machine (1) comprises a drive (8) configured to drive the chassis in order to move the floor cleaning machine (1) over the floor surface (7), and the drive (8) being switched off if the first or the second fault signal is present.
 6. The method according to claim 1, the floor cleaning machine (1) being designed as an autonomous floor cleaning machine (1).
 7. The method according to claim 1, wherein the cleaning-liquid container (17) and the cleaning means (9) are connected by a cleaning-liquid pipe (15) for the purpose of supplying cleaning liquid, and a flow sensor (21) is provided, in the cleaning-liquid pipe (15), as a means for sensing the amount of cleaning liquid supplied in the first time interval.
 8. The method according to claim 1, wherein the cleaning-liquid container (17) and the cleaning means (9) are connected by a cleaning-liquid pipe (15) for the purpose of supplying cleaning liquid, and a cleaning-liquid pump (23) being provided, in the cleaning-liquid pipe (15), that is designed to sense the amount of cleaning liquid supplied to the cleaning means (11) in the first time interval, such that the pump (23) acts as a means for sensing the amount of cleaning liquid supplied from the cleaning-liquid container (17) to the cleaning means (11) within a first time interval.
 9. The method according to claim 1, a first means (27, 29) being provided for the purpose of sensing the level (25) in the cleaning-liquid container, and the amount of cleaning liquid supplied in the first time interval being sensed, by the first means, by sensing of a change in the level (25) in the cleaning-liquid container (17) in the first time interval.
 10. The method according to claim 9, the first means (27, 29), for the purpose of sensing the level (25) in the cleaning-liquid container (17), comprises a float (29), the change in the position of the latter in the first time interval being sensed in order thereby to sense the amount of cleaning liquid supplied in the first time interval.
 11. The method according to claim 1, a second means being provided, for the purpose of sensing the level (43) in the dirty-liquid container (33), and the amount of cleaning liquid supplied in the first time interval being sensed, by the second means, by sensing of a change in the level (43) in the dirty-liquid container in the second time interval.
 12. The method according to claim 11, the second means, for the purpose of sensing the level (43) in the dirty-liquid container, being designed as a pressure sensor (39, 41).
 13. A floor cleaning machine designed to execute the method according to claim
 1. 